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 Post subject: Philco Tapped Volume Control
PostPosted: Dec Thu 09, 2010 11:02 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 202
Location: california
Hi Everybody
I have a Philco 37-630 that needs a new volume control pot. I haven't been able to find the exact part anywhere and want to come up with an alternate method. The schematic says the pot is 2 megs with a tap at 1 meg that goes through a 51k resistor to ground. If the slider is restricted to just the first 1 meg then I can replace the 2 meg with a 1 meg and add a 1 meg resistor to ground. I don't believe it is like this though or Philco would have used that method to begin with because it would be cheaper. It looks to me if I do it with the 1 meg pot and 1 meg resistor that I won't be able to turn the volume all the way down although pretty low. I am sure someone has solved this problem before and I would appreciate any help you can give me.
Thanks,
Jim


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 Post subject:
PostPosted: Dec Thu 09, 2010 11:27 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 31464
Location: Livermore, CA
Hi Jim

In your radio I would connect the resistor to center terminal on the replacement volume control. One side of volume control connects to ground.

You could just leave the tap resistor disconnected but then one position on the tone control wouldn't work.

Here is a 630 schematic. (One year before 37-630)

http://www.nostalgiaair.org/PagesByMode ... 013811.pdf

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Norm


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 Post subject:
PostPosted: Dec Fri 10, 2010 12:04 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 202
Location: california
Hi Norm
Thanks for the reply. Now I can see how the tone control is wired in. I wondered why I couldn't find a 37-630 schematic at Nostalgia Air. With my tin ear the tone control doesn't make much difference so I can just leave it out. If the two positions were labled bass and treble and I left the tap out I would have the treble position left, right? Left, right. Sounds like army talk.
Thanks again,
Jim


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 Post subject:
PostPosted: Dec Fri 10, 2010 12:24 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4395
Location: St. Louis, MO, USA
I'd think you'd be better off just forgetting about the extra 1 meg resistor. If you add it in on one end of the pot you won't be able to turn the volume down low enough, and on the other end you won't be able to turn it high enough for those faint shortwave signals.

Although using a 1 meg pot instead of 2 meg pot would have some theoretical significance, I think anyone would be really hard pressed to notice any difference from a practical standpoint. Connecting the 51K resistor to the center tap would be, as Norm says, your best bet if you can't find a pot with the extra tap.

Alternatively, Mark Oppat at www.oldradioparts.net is often able to come up with the correct pot with the extra tone compenpsating tap. He has a large store of such controls.

According to philcoradios.com the 37-630 was quite similar to the 37-620 with the exception that yours has a shadow meter.

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Terry Davidson


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 Post subject:
PostPosted: Dec Fri 10, 2010 1:04 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 202
Location: california
Hi Terry

I found the 37-620 schematic and it looks very much like the radio. If I don't use the tap I will just use a 2 meg pot without a tap which doesn't seem to be hard to find.
Thanks,
Jim


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 Post subject:
PostPosted: Dec Sat 25, 2010 8:29 pm 
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Joined: Nov Sun 25, 2007 9:40 pm
Posts: 223
Location: Fallbrook, California
Jim,
I have the control you need. Come by and I'll give it to you. I'm in fallbrook. PM for my address and phone number.
Mike


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